This invention relates to a hydraulic impact device or a drifter device provided with an improved power transmission unit for transmitting the rotation of a motor to a shank rod.
There has so far been employed a crawler vehicle mounted drill provided with a drifter device adapted to give impact and rotation to the shank rod when drilling rocks or the like. The prior art drifter device comprises, for example, a shank rod which is rotatably and reciprocably mounted on the leading end of the drifter body, and is arranged such that a striker piston reciprocated by a hydraulic unit gives an impact force to the shank rod and a rotational force is transmitted by a rotary motor through a power transmission means to the shank rod. The conventional power transmission means have been constructed such that the rotation of the rotary motor can be transmitted from a gear to a sleeve and then through bolts and knock pins to a chuck which is engaged by splines formed thereon with the shank rod. For this reason, the bolts tend to get loose in operation resulting in fracture of the bolts and/or the knock pins, and therefore such troubles as the rotation of the motor cannot be transmitted to the shank rod have so far occurred frequently.